1. Field of Invention
This invention relates to vision correction methods and an apparatus which uses a biofeedback approach and brain wave evaluation while simultaneously monitoring eye movement, evaluating the eye-movement function for interference, and establishing a trend.
2. Description of Prior Art
Amblyopia--the loss of vision due to "disuse" of the eye(s)--is the most common cause of visual loss in American children (Krueger and Elderer, 1984). It is caused by inadequate visual stimulation of the brain during the critical period of visual development. The most common cause of amblyopia is strabismus--misaligned or "crossed" eyes. Primary strabismus leads to amblyopia through the neural mechanism of suppression, because the brain ignores images coming from the crossed eye. About one-third of all persons with strabismus are diagnosed for amblyopia (Elder, 1994). Strabismus and amblyopia affect about 5% of the population (Nelson, 1984). Sensory strabismus results from any primary cause of visual loss. If vision is poor in one or both eyes, fusion (the brain's ability to use both eyes together and thereby attain and maintain depth perception) cannot occur and ocular alignment is lost due to a partial loss of brain control. The treatment of strabismus is aimed at: 1) eliminating amblyopia; and 2) realigning the eyes to restore binocular perception.
In ophthalmology both surgical and non-surgical (or functional) methods are applied for treating strabismus. The surgical methods demonstrate fast and radical results, but there are many contra-indications for surgery such as high occurrence of complications and, most of all, possibility of reoccurrence of symptoms of strabismus after surgery. Thus, there is no reasonable basis for the preference of surgical methods.
There are two groups of non-surgical methods used for treatment of "crossed" eyes: occlusion methods and those using a biofeedback procedure. Until recently the most effective non-surgical method for treating of strabismus was occlusion. This method is based on the occlusion of the dominant eye by patching and thereby forcing the crossed eye to perform the visual function. The origination of this procedure goes back to the 18.sup.th century (Saint-Yves, 1722. Cited in Hischberg, 1984; Buffon, 1743. Cited in Wilkinson, 1943).
The occlusion therapy alone (Elder, 1994) or in combination with pharmacological treatment (Kubota and Usui, 1993) has an efficiency in the range of 40-70% and is not entirely successful (Flynn and Cassady, 1978). For most effective results, the occlusion treatment must be made during the first 6-7 years of the person's life. As a result, this generally limits the effective use of these methods to young children. The treatment also should continue for up to 2 years. The duration of treatment is deemed as a burden and an inconvenience. There is also very high recurrence of strabismus after treatment is discontinued. In addition, because these children and young adults are in their formative years, they continue to participate in school and engage in other normal social activities. As a result of their reduced visual function, however, such participation can lead to distress and a decision to discontinue further treatment. There are also cosmetic concerns and concerns about allergies to certain types of patches used for occluding vision.
Another treatment method is biofeedback therapy. This is a technique which is based on conditioning principles and has been used in a variety of applications. The technique provides a person with immediate information from the biological process which normally is beyond his conscious awareness, thus facilitating voluntary regulation of these same functions. The methods for vision correction based on a biofeedback procedure can be divided into two categories. The first method is targeted on the improvement of visual acuity of the eye with a misaligned optical axis. The methods falling in the second category use autotraining to develop endogenic reflectory mechanism in order to reduce the degree of optical axis misalignment in the crossed eye.
Both methods are based on theoretical assumptions similar to those in the occlusion therapy. It is assumed that the occlusion of the dominant eye during the treatment procedure inclines the eye with reduced visual function to participate actively in visual perception. The improvement of visual acuity in the treated eye, the theory continues, leads to gradual recovery of the binocularity (and visa versa for the second method) and the increased control over the oculomotor muscles by the central nervous system. This results in restoration of the optical axis and the cure of strabismus.
Among applications subscribing to the first method is the Russian Federation Patent 2070011 to Tumanyan (issued Dec. 10, 1996) disclosing the method of visual function correction specifying amblyopia treatment. This invention suggests the approach for treatment of amblyopia by the restoration of vision acuity. This method uses detection of the person's electroencephalogram (EEG) with computer analysis performed after amplification of the signal. The distinctive feature of this method is the use of spontaneous fluctuations of EEG alpha-waves as a factor controlling the switch of a movie being viewing by a person. The spontaneous intensification of EEG waves is considered as a sign of the relaxed state of the brain structures connected to visual functions. In contrast, the decrease of the intensity of EEG alpha-waves indicates visual cortex activation. In presence of myopia (nearsightedness) and a diagnosis of the anisomyopic amblyopia the spontaneous occurrence of brain relaxation (correspondent to the increase of the intensity of EEG alpha-waves) is considered as a positive trend and is encouraged by an opportunity to watch the movie. In situation involving hyperopia (far-sightedness) and a diagnosis of the anisohypermetropic amblyopia or the strabismic amblyopia, the activation state of the brain (correspondent to the decrease of the intensity of EEG alpha-waves) is supported. The described biofeedback procedure is repeated daily for 20-30 minutes during 20 days (this is referred to as one course). The results of the treatment with this technique are discussed below.
U.S. Pat. No. 4,896,959 (issued Jan. 30, 1990) to O'Brien discloses a visual acuity unit for treatment of amblyopia through the use of a solitary visual target maintained at a level of minimal discernible size. This method is limited only to use by persons with a lack of acuity which is not of a refractive or transparent nature. Young persons would have difficulties using this apparatus because of its complicated nature and the associated tasks to be performed. Also, it would have the same difficulties associated with persons having amblyopia and severe degrees of strabismus. The same is true for other methods which employ only a training of the acuity of vision without a restoration of the alignment of the optical axis.
An example of the second method used for biofeedback therapy was described in (Goldrich, 1982). In this method persons were trained to achieve and sustain alignment of the optical axis by receiving an audio-feedback signal. The eye position was monitored with an instrument using a spectacle frame holder with a pulse-rated infrared (IR) emitter diode and two rated IR photo cell detectors in front of each eye. Detection of lateral eye movement was limited to about 0.5 degree. The changes in ocular vergence movements were recorded, amplified and outputed to the voltage-regulated audio oscillator. An audible tone of variable pitch could be heard as the eyes behind the IR detectors assumed different vergence positions. The more extreme the vergence position the higher the pitch. Different optical charts (e.g., Snellen letters and other reading material) have been used as visual stimuli. Therapy was administered in weekly hour-long sessions with frequent brief rest periods. The results are discussed below.
A similar approach is disclosed in U.S. Pat. Nos. 4,533,221 and 4,660,945 to Trachtman. The method to train a person to improve visual focusing ability has been suggested. Analogously to the method described by Goldrich, the refraction of the eye was measured and used to produce a tone to which a person may be trained to respond by driving up the pitch. The eye refraction detection during the therapeutic session requires a long-time fixation of the head which renders this kind of treatment almost impossible for children. Moreover, the refraction of the eye does not describe synchronizing eye movement of both eyes which is important, especially for treatment of persons with strabismus. Also, audio-tone used for a biofeedback signal is not the optimal choice for young children.
U.S. Pat. No. 5,374,193 (issued Dec. 20, 1994) to Trachtman discloses the method and apparatus for training to remain in alpha-state (then the brain emits alpha-waves) using the EEG for the brain state evaluation and using EMG for muscle tension detection. Improved methods of reflected-back radiation from the eye detection incorporating a two-dimensional CCD matrix has been used. The EMG has been used for relaxation training. Such training to remain in the alpha-state may be useful for vision improvement in adults, but much less effective in young persons due to their having poorly expressed alpha-waves. The application of this method requires the long-time fixation of the head to a holder. This is physically inconvenient for a person, particularly one of tender years.
Russian Federation patent 2061508 to Mikhailenok (issued Jun. 10, 1996) based on the USSR Inventor's Certificate 1688867 (Jul. 8, 1991) discloses the method of functional correction of neuro-muscular dysfunction (e.g., poor posture, scoliosis) and spasm of accommodation in ophthalmology. In this method the person's bioelectric activity of the brain (EEG) or the muscle (EMG) is detected. Then the signal is analyzed with a computer algorithm and the decision to let the person play a video-game is made based on the results of the analysis. The distinction of this method is in the use of a video game as an attractive goal for children. Previous methods generally used audio signals or other means which do not interest or stimulate children stimuli thereby resulting in a lower efficiency rate of the treatment.
U.S. Pat. No. 5,363,154 (issued Nov. 8, 1994) to Galanter discloses computer based vision training method and apparatus.
None of these devices and methods has incorporated the unique features of the present invention. Our invention incorporates a new method and an apparatus to restore visual function in the misaligned eye by controlling movements of the eyes in conditions close to the natural process of visual perception (e.g., watching a movie or playing a game) with the simultaneous encouragement to increase a visual acuity.
The disadvantages of prior applications include:
a. Surgical methods, although fast and radical, have many contra-indications, lead to complications in post-surgery period, and do not eliminate a possibility of a recurrence of strabismus. PA1 b. Occlusion therapy is not quite effective and also has a high recurrence rate. It must be started at very early age and continue for up to 2 years leading to distress at school and precluding the child's participation in many activities because of his greatly reduced visual functions. There are also cosmetic concerns and possible allergic reactions. PA1 c. Known methods of biofeedback therapy based on the restoration of visual acuity of the eye with a misaligned optical axis are only about 50% effective. This is due in part to inadequate choices of the EEG components for the brain state evaluation. The brain alpha-waves used in these techniques are poorly expressed in young children with low visual function and therefore provide no opportunity for efficient and effective analysis. This in turn limits the application of methods employing analysis of brain alpha-waves (R.F. Patent 2070011 to Tumanyan; U.S. Pat. No. 5,374,193 to Trachtman). PA1 a. to provide an easy-to-use apparatus for training for simultaneous improvement of visual acuity and realignment of the optical axis therefore taking into account needs of persons with different forms of strabismus and amblyopia; PA1 b. to avoid different side effects caused by invasive methods and permanent patching of the defect eye; PA1 c. to describe visual function of the defect eye by dynamic spectral analysis (Fourie analysis) of alpha-, beta-, and theta-waves detected in the person EEG while avoiding artifacts caused by the age of the person and to improve the quality of description of the brain visual activation function compared to methods limited to the use of only the alpha-component of brain waves; PA1 d. to take into consideration the individual characteristics of the person by analysis of the person eye reaction to an unstructured image and to a structured image of the same brightness and by calculating individual coefficients for visual function analysis; PA1 e. to evaluate the synchronism (including time, direction and amplitude) of the eyes' movements by detection and analysis of the person's electrooculogram (EOG) of both eyes and providing a novel way to characterize eyes' movement function and avoid long-time fixation of the head and other inconveniences for the person; and PA1 f. to use the electromyogram picked up from m. orbicularis oculi in order to account for any interferences caused by blinking.
For example, using the method described by Tumanyan (Russian Federation Patent 2070011) a better efficiency of the treatment has been observed in persons with anisohypermetropic and strabismic amblyopia (about 70%) whereas for persons with anisomyopic amblyopia the efficiency was about 45%. The remission after 1-2 courses of the treatment was considered a successful treatment. Taking into account the frequencies of occurrence of different forms of amblyopia, total efficiency was about 55% (Tumanyan et al, 1993). A rather low efficiency of this method for treating anisomyopic amblyopia corresponds to how EEG signals are expressed and analyzed. The EEG alpha-waves used for the brain state evaluation in this therapy are poorly expressed in young children (3-5 years old). Children suffering from amblyopia exhibit even weaker alpha-waves than their healthy counterparts, which makes analysis of the EEG alpha-waves almost impossible. Older persons generally have better pronounced alpha-waves, but treatment in this group is less efficient. Wrong position of the eye with misaligned optical axis is already fixed in older persons and their CNS is unable to sufficiently control the visual function of this eye. In addition, the oculomotor function of the eye is not analyzed in this method.
Second, this kind of therapy has a low effect on persons with severe degrees of misalignment of the optical axis (severe strabismus). This can be explained by the inability of the person's CNS to control visual function in the "crossed" eye without normalizing its optical axis.
Among the methods discussed above, those described by Trachtman (U.S. Pat. Nos. 4,533,221, U.S. Pat. No. 4,660,945 and U.S. Pat. No. 5,374,193) provide a detection of the refraction of the eye to evaluate movements of the eye. But this method lacks the complete description of the eyes' movement function (e.g. it is impossible to detect synchronization of movement because the refraction from only one eye is detected). Also, the use of audio-signal for a biofeedback connection is not an optimal choice.
The biofeedback procedure for developing a reflex mechanism in order to reduce the degree of optical axis misalignment was unsuccessful for persons with significant loss of vision and/or severe degrees of misalignment. A low visual acuity results in the failure of the CNS to control the amblyopic eye's visual function including the alignment of its optical axis. Therefore, without improvement of visual acuity, the misaligned eye is unable to restore the connection between the CNS and the eye which is necessary to achieve realignment of the optical axis. Also, the audio-feedback signal used in this therapy is not interesting for children. This makes it difficult to obtain their full participation in the procedure. In addition, as previously described, the manner in which eyes movements are detected in this technique is not very comfortable for a person.
For example, the training described in (Goldrich, 1992) was about 80% efficient for persons with mild degrees of divergence of the eyes. These persons usually have sufficient visual acuity to be able to control eye movements. However, for persons with significant loss of vision and strabismic amblyopia a positive result was achieved only in about 20% of cases. Moreover, these results were unstable. The failure to cure persons with low vision by this therapy is explained by an absence of preliminary improvement of visual acuity in the misaligned eye. It is known that low visual acuity in the amblyopic eye is connected to the failure of the CNS to control this eye's visual perception including the alignment of its optical axis. Therefore, without attempts to improve the misaligned eye's visual acuity and restore CNS control of visual function these methods are very unlikely to realign the optical axis. Thus, persons with severe strabismus are not helped by this kind of therapy. Besides the neurophysiological explanation, it is reasonable to consider alternate methods to stimulate the person in his attempts to maintain the eyes in correct alignment. To gaze on a motionless point is not a physiologically correct task for an adult and it is especially difficult for children. Also, for very young children, it is difficult to obtain full participation because of their lack of interest.
Accordingly, several objects and advantages of the present invention are:
Further objects and advantages of the present invention include providing a system for vision correction which can be used easily by medical personnel and be convenient for persons as will become apparent from a consideration of the drawings and ensuing description.